


One Girl in All the World

by astronavigatrix



Category: Adventure Time
Genre: F/M, aka fuck diplomacy, in which Fionna is a bargaining chip and PG can't do a thing to help, let's just punch monsters in the face until it works out, seems legit right?
Language: English
Status: In-Progress
Published: 2014-07-06
Updated: 2014-07-08
Packaged: 2018-02-07 15:44:39
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 4,532
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1904628
Author URL: https://archiveofourown.org/users/astronavigatrix/pseuds/astronavigatrix
Summary: <blockquote class="userstuff">
              <p>A modern Adventure Time AU BTVS-style involving a vampire, a fairy prince, a Slayer-in-Training and one slightly too-sassy <s>scaredy-cat</s> Watcher.</p>
            </blockquote>





	1. I just need a compass and a willing accomplice

When you’re more or less barely over five feet tall, people tend not to take you very seriously.   
  
It’s the first mistake people tend to make when dealing with her, the second one being, almost always without fail, the fact that the words that follow are usually along the lines of:   
  
"Stay out of this, sweetheart-"  
  
She takes hold of the hand that comes out, intending to push her back and away, out of sight and out of mind where- she assumes, at least- he thinks she belongs. Before he realizes it, she’s wrapped her fingers around his hand, dainty structure not stopping calloused fingers from pressing hard into the webbing between thumb and fingers. She takes a step forward then under, half-turning to give the turn some real leverage. The next step has a foot rising to push into the back of his knee, her free hand pushing forward on the other shoulder, furthering the loss of balance. He stumbles, fights it, but still goes down easily.  
  
Fionna bares her teeth in a vicious, victorious grin.   
  
"Look, you started this, but I’m not scared to finish it, guy."  
  
The guy beneath her sputters, trying to shake her off but finding the motion pulls on his shoulder in a way that is nowhere near pleasant, and instead settles for trying to glare at her over his shoulder.  The stupidly long hair on that side of his face covers his eyes, but it’s an attempt— though his glare is soon enough directed back at the other half of the conflict, who claps his hand delightedly, giving a low whistle.  
  
"Check out the moves on  _you_  Bunny…!”   
  
"You’ll be seeing them up close and personal next if you don’t learn to  _shut it_ , idiot!”   
  
The young man across from them raises his hands in mock-surrender, mouth curling up at the corners in a way that does distinctly unfair things to her stomach, grey-green eyes crinkling in obvious amusement even as he takes a swaying step backward. Still glowering, she pulls the first guy up and pushes him toward the door, his girlfriend hesitating before following suit, and shoves him out the door. He moves as if he’s going to shove past her again, but Fionna squares her shoulders and lifts her chin, eyes narrowing, and he reconsiders with a surprisingly wide-eyed look that’s more afraid than she’s used to. Her game face must be getting better.    
  
She doesn’t realize that it’s because the other participant in the fight had slunk out of the shadows behind her and bared too-sharp teeth at him as his eyes turned pitch dark.   
  
He’s all charm and smiles when she turns and nearly runs into his chest, and he swoops down and slides an arm around her waist, eyelids low and purrs “my hero” in what she knows is meant to be a seductive tone, leaning in far too close and looking at her far too intensely.  
  
Fionna slugs him right across the jaw and she hears Cake groan from behind the bar as he drops like a sack of potatoes.  
  
By the time she stops blushing and realizes she’s laid out a customer (even if he was a slightly drunk, slightly too-flirty one) Cake is already moving to help her pick him up and cart him to the couch in the back, eyes rolling.   
  
"Fi baby, you really need to keep working on pulling your punches."    
  
Between them both, Marshall Lee continues to fake being unconscious, holding in a groan at the fact that the Slayer he’d come to get rid of is the cute little thing he’d been flirting with at the bar. 


	2. I'm Always on a Mission from the Get Go

Laid up in the back room of the bar- in what he assumes is the employee lounge considering the coats and purses in one corner- Marshall Lee felt his chin begin to bruise even as his physiology began to heal it. He knew, of course, how strong Slayers could be; he’d taken out more than his fair share of them in his thousand or so years of life. Never before had one hit him hard enough that the injury began to show faster than his body could fix it. It was exciting, realizing that he might have a real fight on his hands for once.

But it also meant that his Mother was right. This Slayer could prove to be too dangerous to be allowed to live for much longer.

He sat up as soon as the door shut behind her, lights dimmed- so as not to hurt his eyes in case he woke up, he assumed- and ran a hand through his hair, wondering just how he’d gotten himself into this mess in the first place.  
  
Honestly, he was pretty sure it was all Gumball’s fault.  
  


________________________

 

Killing Slayers was nothing new to the self-proclaimed Vampire King. Honestly at one point in his life, it had been something of a hobby. Let the Slayer get old enough, experienced enough, _cocky_ enough to be a challenge, then show up and prove to her and the Watchers that she was, in fact, _not_.  
  
He’d never been _ordered_ to kill one before though. And definitely not by his own mother.  
  
So imagine his surprise when he’d woken up one cloudy evening to find a Portal open and the Abadeer herself peering down at him. _Smiling._ At least, he assumed it was supposed to be a smile. Her bright red eyes were too wide, her lips pulled too far back and exposing not only her gums, but twin rows of needle-sharp teeth that were entirely too numerous to even remotely pass as human. The fact that her hair was pulled back tight enough to make the expression seem like it had been frozen into place didn’t help in the slightest.  
  
Marshall Lee would not have been proud to say that he’d shrieked like a grade school child that had watched the wrong horror movie, but that only prompted the Abadeer’s smile to widen further, straightening and turning sharply on the thin heels of her black pumps as he jolted into a seated position where he hovered over the sheets of his four-poster bed.  
  
“Honey please- you sound like you’ve never seen a demon before!”  
  
“No, mom- I sound like someone who’s woken up to the flippin’ Lord of all Evil _leering_ at them in their bed, _that’s_ what I sound like!”  
  
Voice sleep-rough and sluggish, he managed to sound more petulant than irritated, and the Abadeer dismissed his words with the wave of a hand, the other tucked behind her, her bearing almost military-stiff, as she paced.  
  
“You were sleeping so long, I was worried there might be something wrong with you. I was five minutes from dragging you to see my _personal_ physician back home you know!”  
  
Her words sounded concerned, and were Marshall five-hundred years younger and several dozen points dumber, he might have believed her. Her ‘concern’ was only thinly-disguised opportunism- an excuse for a reason to try and drag him back with her through the literal Hellhole she’d crawled out of. So he rolls his eyes at her, making sure she can see the red of his irises stark against the black of his eyes, and throws the blankets off as he finally deigns to get out of bed. He dips dangerously toward the floor but eventually hovers into his usual repose, hands crossing across his stomach and hair falling lazily into his eyes as he gives his mother the mildest look he can manage.  
  
“What do you _want_ , Mom?”  
  
“Now Marshall, really- I come all this way and you assume I want something?”  
  
His dull stare is his only response, and the Abadeer rasps out something that might be a laugh, if laughter sounded like someone grinding bones with a mortar and pestle. The sound almost sends a shudder down his spine, but for the sake of not giving her an inch to work with, he restrains it with every bit of willpower he’s got, waiting for her to stop and then prompting her to speak with a faint motion of one arm. She does stop, and immediately straightens, pinning her eyes on him in a sharp, unblinking stare- the way she always does when she’s going to say something he’s either going to love or absolutely _hate_.  
  
“We’ve been receiving… reports, lately. Vanquished demons, slain vampires, that sort of thing, and the thing is… they’re not the usual low-level lackies. I mean just the other day I heard tell that Japhrimel didn’t even get two hours in her possessed body before she was Cast Out!”  
  
The way she says things, he’s not entirely sure if she’s furious or elated- knowing her, it’s probably a bit of both, and she steps closer to him as she speaks, both hands clasped behind her back, eyes widening further.  
  
“Now normally, I’d say it’s their own fault, being bested so easily, _but_ -!”  
  
There’s always a ‘but’ he thinks, but wisely keeps his mouth shut, straightening slightly so he looks like he’s propped up on his elbows, expression getting more and more bored.  
  
“It’s all too fast, the pits are getting even _more_ overcrowded, and while normally I wouldn’t mind, the more demons are in the pits, the fewer that are up here tempting and defiling and causing all that lovely chaos that nets me so many lovely, yummy, _mortal_ souls.”  
  
Which, as Marshall knows, is bad not only for business, but for her in particular, seeing as how she sustains herself on them, from time to time. An Abadeer without souls to consume, especially fresh mortal ones, isn’t much of an Abadeer at all.  
  
“So? Send one of your minions to deal with the problem. Isn’t Pazuzu good with interference?”  
  
“Oh but I have! And they haven’t really stood much of a chance. I’ve got to say, if this keeps on, this little Slayer may actually become a serious problem.”  
  
The word ‘Slayer’ makes him sit up, and the Abadeer’s smile returns, sly and smug.  
  
“So I figured, since my little monster does _so_ like playing with them… Why not ask you to take care of her? After all, it’s been a while since you sent one down, hasn’t it? They’ve all been dying so young, the poor things…”  
  
It is, he thinks, something of a shame- they just didn’t make Slayers like they used to. But if the new one is really that good…  
  
“I guess I can go take a look.”  
  
His mother looks entirely too delighted at his compliance, and he thinks he’ll probably take a good long while getting it done, just to annoy her, and reaches out to squeeze his shoulder. Her grip would have broken a human’s shoulder, but it only leaves the faint imprint of her long, taloned fingers on his skin for a moment before it disappears and he gives her another flat, irritated stare.  
  
“That’s a good boy- I knew I could count on you to get things done! Maybe when you finish we can celebrate at the castle! I’ve got these new servants that-“  
  
“Not a chance, mom.”  
  
Her lips press thinly together, her smile more of a grimace now, and her eyes burn far too bright.  
  
“That’s no way to speak to your mother, young man.”  
  
He looks uncomfortably away, but hides it by shrugging and rolling his eyes once again, turning to float away from her, waving a hand in dismissal.  
  
“Whatever. I’ll deal with the Slayer, no problem.”  
  
His mother’s low, thoughtful sound draws his attention back to her, but by the time he looks over his shoulder, the portal is already closing behind her, leaving her parting words hanging in her wake.  
  
“It better not be. I’m afraid I won’t be able to overlook a failure.”  
  
And he may not like his mother most days, but in that moment, he’s pretty sure he might actually hate her.

 

 ________________________

 

“I need you to help me find a girl.”  
  
“Why hello Gumball, how _have_ you been, Gumball? Anything new going on in your life, Gumball? Oh, Marshall Lee, how kind of you to ask- I’ve just been _running an entire kingdom_ , nothing important! I can certainly drop everything to help you find a girl to-!”  
  
“Can it, powder puff, it’s not like that.”  
  
Prince Gumball could, ostensibly, be called Marshall Lee’s best friend. He could, sadly, also be called Marshall Lee’s _only_ friend- vampires are not creatures that deal well with others by nature, and demons never tend to last long, carried away by their desires as they often are. Marshall, being an unholy and wholly unpredictable combination of the two, is disgustingly social… when he wants to be. Gumball, on the other hand, is almost as reclusive as any vampire, but having the misfortune to have been born royalty, he hardly gets as much solitude as he would like. But he grins and bears it for the ragtag remainder of the Fair Folk that fall under the protection of his makeshift ‘kingdom’. Luckily, it doesn’t actually require as much minding as he likes to pretend, and now and then he’s lucky enough to be able to take a few days off to himself.  
  
He really doesn’t want to use the time he can likely spare in the coming weeks on Marshall Lee, but he can already feel the chances of that growing slimmer.  
  
“So then what _is_ it like? And make it fast, would you? I have a delegation arriving from the espers in the next town over in order to try and organize some camouflage for a new section of the Kingdom.” He asks, of course, against his better judgment, retreating back into the penthouse that serves as the center of his kingdom, the building beneath it more or less both castle and kingdom in equal parts. “This isn’t going to involve any felonies, is it?”  
  
“Only a couple minor ones. Maybe.”  
  
Marshall Lee floats after him, picking up the edge of the thick drapes that cover his windows before sinking a fang in. The color drains away and Gumball stutters and shoos him away with flailing arms, wings fluttering into vision irately behind him, the glamour that would normally conceal them dropping as the prince’s ire rises.  
  
“Do you have any idea how much those cost?”  
  
“Nnnnnope. But they were a little bland. Next time, pick a brighter color why don’t you?” A long, meaningful look at the pinks and purples that made up the rest of his private quarters, and he turned a dry look on the prince, brows tilting slightly upward. “Not like everything else in here isn’t already eye-searing.”  
  
“Did you come for _information_ , or just to criticize?”  
  
“No one said I couldn’t do both- the latter’s just a pleasant surprise for everyone.”  
  
Gumball clenches his jaw so hard, Marshall is surprised he doesn’t hear anything crack, and the vampire laughs and settles onto his side in midair, cheek propped up in his hand as he waves a hand at him, fangs pressing against his lower lip as his mouth curves up into his usual smug smirk.  
  
“Alright, alright. Don’t get your wings in a wind, Gumbutt, look. All I need is some info on the new Slayer. Rumor has it you know the girl, and I kinda—ohhhh…”  
  
At the mention of the Slayer, Gumball’s previous irritation had melted from his face completely, replaced with something more like worry. Maybe even fear. The expression is gone almost as quickly as it comes, and Gumball’s expression settles into the icy neutrality he tends to save for Official Business. This, Marshall thinks, is going to be _fun_.  
  
And by ‘fun’, he of course means ‘terrible’. He should have known better when his mom didn’t just send one of her bigwigs after the girl. Killing off a Slayer is one thing, but killing off an official Champion of a Kingdom that is a part of the Supernatural Royal Council is… well. It’s a bad move, politically speaking- on more than just the level of seeming as if you’re trying to weaken another kingdom. Champions are the ones who take Challenges for their Kingdom, who prevent wholesale war from sparking between different factions of the supernatural world. To kill one in cold blood instead of in challenge is as good a way to set every other kingdom against you as killing the Kingdom’s royalty. Not to mention a good way to get yourself _killed_.  
  
And if he doesn’t manage to kill Gumball’s, his _mom_ is going to kill him instead.  
  
Oh he is so very, very boned.  
  
“I didn’t believe it when I heard it but I’ll _be_. So you really _did_ pick up a mortal as your Champion. And a Slayer no less… man, the Council must be _pissed_ …!” A velvety chuckle escapes him, and he’s thankful it doesn’t sound forced as he rolls onto his stomach in midair, ankles crossing and chin settling in his hands like a teenager gossiping at a sleepover. “I’d be impressed if this wasn’t about to become so hideously awkward!”  
  
“You won’t lay a hand on her, Marshall. You _can’t_. The Council will…”  
  
“The Council will sentence me to death and turn against my kingdom blah blah _blah_ … yeah. I know. But seeing as I’m kind of a free agent, I don’t really _have_ a kingdom. So, you know, no repercussions for anyone but me.”  
  
His tone, against his better judgment, turns just a little bitter at the end, and he’s sure that Gumball immediately understands the situation from the way his glare softens into a glower, eyes lowering sadly.  
  
“As long as you understand. Regardless, I’m afraid I can’t give you any information. Fionna— _my Champion_ is not someone whose trust I will betray. Not after what she’s pledged to me. You understand, I’m sure.”  
  
“Fionna, huh?”  
  
Gumball stiffens again, wings halting their slight, idle flutters- every line of him goes absolutely still, and it’s obvious he’d been hoping Marshall hadn’t caught the slip.  
  
“Well, I make no promises, but hey. She doesn’t have to know you’re the one who helped me find her, right?”  
  
“So help me, if any harm comes to her-!”  
  
Where Marshall Lee had been floating, there is suddenly only a writhing dark mass of eyes and teeth and tentacles, the last of which curl around him and squeeze as the main body of the creature looms darkly over him, glaring with bright, bright red eyes.  
  
Then he’s dropped, and Marshall Lee, once again in his vampire form, drifts idly toward his window, offering a two-finger salute over his shoulder.  
  
“You won’t do a thing.”  
  
And it’s not because he won’t want to, but because Prince of the Fair Folk or not, Gumball really wouldn’t stand a chance against him.

 

 ________________________

 

 

He spends the next week looking for every ‘Fionna’ he can find listed in any phonebook, any social network, any listing at all he can get his hands on, and when he finds her, it’s completely by accident.  
  
The place isn’t quite a restaurant and isn’t quite a bar, and it’s definitely not a club, but it’s got enough of all three that it draws crowds that come for the novelty and stay for the atmosphere and the food both. The girl he’s followed there- Fionna Mertens is the name he has- is an average-looking girl with a less-than-average IQ and an above-average rack, and while the latter might be enough to make up for her startling lack of brains for some, it doesn’t quite work for him, and he gets bored of pretending to flirt with her in no time.  
  
“You gonna order, or are you just gonna sit there and look really depressed about our beer selection?”  
  
The voice that pulls him from his thoughts is teasing and light, and he raises his head from the menu he’s been using as an excuse not to make conversation with anyone around him to snap ‘what selection?’ only to shut his jaw on his tongue in surprise. The pretty blonde staring at him from behind the bar flushes a little as she finally gets a look at his face (it’s not the first time it’s happened tonight and it won’t be the last) but gives him an easy grin and leans forward a bit.  
  
“I’d give you a suggestion, but beer’s not really my thing.”  
  
He recovers from biting his tongue and gives her his most charming grin in return- she actually leans back from the bar and fusses with the white bandanna holding her long blonde hair in a messy bun to pretend she’s unaffected, but he can see the color on her cheeks deepen- and purrs-  
  
“And yet you’re standing behind the bar slinging drinks.”  
  
“Yeah, funny how that works out, huh?”  
  
She laughs nervously, pushing her bangs away from her face in a way he’s only ever seen guys do- absent and rough- and when she settles into a smile again he realizes that with the ends of her bandanna sticking up like they are and the buck teeth that little grin displays, she looks somewhat bunny-like. The look is a lot more innocent than what he’s usually into, but the smile and the energy coming off her is infectious, and he finds himself smiling along with her.  
  
“Alright then, what would you recommend?”  
  
She blinks in surprise, as if she hadn’t been expecting the question, and then her grin returns,  wider and brighter than before, and she leans forward again, seeming to forget that she was flustered enough to pull away in the first place.  
  
“Well, what do you like?”  
  
He winds up with a strawberry-flavored drink that’s almost atomic in color, two bright red berries on one side- he’d mentioned he liked them a lot- and then she’s off to the other end of the bar, summoned by another patron, but his eyes stay on her. At least, they do until Fionna settles across from him, more intent than before on flirting with him now that there’s a considerable amount of booze in her system, and drapes herself against his arm. He’s only a little bit irritated, sipping his drink and looking down at her flatly, until the girl behind the bar looks back at him, sees the girl draped across him, and turns back to the bar sharply, teeth nibbling at her lip.  
  
Marshall decides that Fionna needs to go.  
  
It isn’t hard to convince her to follow him to a dark corner of the dance floor, and it’s even easier to get her to let him nuzzle against the side of her neck. He doesn’t go for blood often, but when he does, it’s never enough to kill. No, that’s how amateurs get caught. He sips from her slowly as he turns them to the slow, thumping beat of the music, one hand at her waist, the other in her hair, keeping the long, dark strands bunched up between his fingers to hide what his mouth is doing. He doesn’t realize how much alcohol is in her system until it’s too late to stop, and he only barely manages to heal the wounds on the side of her neck with a quick lick before a guy pulls her back and away from him, breaking the trance she’d been under, and slugging him across the face. Between the lights, the alcohol in his system from both his drink and more potently Fionna’s blood, and the girl who is now shrieking at the guy swinging at him to stop, that they’re not together anymore, Marshall’s head is starting to pound and his body isn’t processing the booze fast enough to let him retaliate with more than a few too-agile dodges and, near the edge of the dance floor, a good, if not exactly solid, punch to the guy’s ribs.  
  
“Cake, watch the bar!”  
  
“What’chu mean watch the bar Fi that’s why I asked you to- Fi! Fi! Fionna, dammit-!”  
  
His eyes slide back toward the bar as he hears ‘Fionna’ in time to watch the little bunny-toothed bartender slam her hands down on the counter and vault over with impressive ease despite the skirt she’s wearing. She lands, rolls, and is up in less time than it takes to blink, pushing him in one direction with a booted foot, the other guy and his supposed ‘ex’ in the other with both hands.  
  
“Alright now let’s resolve this like reasonable adults- I’m sure what happened is just some kind of misunderstanding and I _really_ don’t want to have to call the cops, so-”  
  
“Stay out of this, sweetheart.”  
  
It takes less than five seconds before she’s brought him down, and really he shouldn’t be so turned on because fuck, fuck, _it’s the fucking Slayer of course_ , and okay her practically breaking a guy’s arm shouldn’t be so _hot_ , but it is and holy shit he can’t do this.  
  
But he’s still drunk, and decidedly stupid and unbelievably impressed with the sheer brutal efficiency of her movements, but all he can manage is a flirty line about her moves as she marches the other guy toward the door. He follows almost instinctively, and he tells himself that it’s because he wants to study her some more, that he’s hoping for a little more violence so he can see what she can _really_ do. At the door, he holds back a hiss at the guy, eyes widening and turning demonic over the top of the blonde’s head, and he should know better than to mess with the mortals like that, but the other guy’s drunk and stupid too and anything he says will be chalked up to drunken hallucinations- if he says anything at all, that is.  
  
When the blonde turns, he’s there, hands slithering around her waist and pulling her close, one push backward from dipping her in his hold.  
  
“My hero.”  
  
And maybe he should have rethought that because she hits _hard_ , harder than he’d been anticipating and between the force and his inebriation he topples like a jenga tower in a sprawl of lean limbs and a now-aching jaw. When the Slayer hooks her arms under his, he knows the call for assistance she gives is for show, but between her and ‘Cake’ he’s carted back into the lounge and set on a sofa to recover.  Cake leaves first, leaving Fionna alone at his side, and she huffs in irritation before muttering ‘ _stupid’_ sharply, though whether to him or to herself is debatable before she stands suddenly, turning away from him.  
  
He doesn’t move only because he’s sure no human would recover from that hit so quickly and for the moment, that’s what he wants her to believe he is.  
  
So here he is, in the back room of a place he hadn’t even meant to be, nursing a bruise from a girl who didn’t even know she should be fighting him, and wondering whether or not he was really going to be able to do this now that his mind was beginning to clear. One thing was still for sure, however.  
  
One way or another, this was still _definitely_ Gumball’s fault.


End file.
